In the automotive industry, it is known that during braking a portion of the reduction in kinetic energy of the vehicle can be harvested and used to generate electricity. Commonly, there are two ways in which regenerative braking is used. The energy of the slowing vehicle can be transferred to a flywheel and stored there. Alternatively, the kinetic energy can be converted to electrical energy through a motor or generator. The electricity can then be stored in a battery or supercapacitor. If the vehicle is not a car but is instead a tram or train, the electricity can be fed back to the vehicle's traction power supply such as overhead power line.
Such systems provide increased efficiency and reduced fuel costs. There is little in the way of such technologies for aircraft.
One known system for generating electricity from the movement of an aircraft is a ram air turbine (or RAT), such as disclosed in GB 2461057. The ram air turbine is a turbine mounted and stored within a compartment of the aircraft. The turbine can be deployed from the compartment by opening a door and swinging the turbine out into the airstream to generate electrical power. Such ram air turbines are deployed in the event of an emergency to provide a back-up source of electrical power. For example, an emergency might be when the main engines or auxiliary power unit of the aircraft fails.
A ram air turbine is shown in FIGS. 1a-1c. FIG. 1a shows the general location of a ram air turbine 10 at the underside of the aircraft fuselage. FIG. 1b shows more detail of how the ram air turbine is deployed from a compartment 20 in the fuselage. FIG. 1c shows the ram air turbine stowed in the compartment 20. In the event of a loss of electrical power, the ram air turbine 20 is deployed by opening a compartment door 30 and swinging the turbine out beyond the skin of the aircraft 5 into the airstream flowing past the aircraft. The airstream rotates the blades of the turbine which drives a generator of the turbine to generate electrical energy. When not in use, such as during normal flight where electrical power is provided by the main engines or auxiliary power unit, the turbine 20 is stowed in the compartment 20 and the compartment door 30 is closed. In the stowed position the turbine is not in the airstream, the blades do not turn and no power is generated by it.
Other attempts have been made to recover energy from the movement of an air vehicle. For example, an energy recovery speed brake has been proposed (see www.airbus-fyi.com/finalists_2011.php) for inclusion in the wing. The speed brake would be a turbine placed between the wing surface and a conventional air brake. However, the small size and location of the speed brake limits the amount of energy that can be generated.
There is therefore a need for an improved method and apparatus for recovering energy from the movement of an aircraft.